Production of butadiene



by-products and carbon,

Patented July 23, 1940 UNITED STATES Peter J. Wiezevich and RaphaelRosen, Elizabeth,

N. J., said Wiezevich now by judicial name Peter J. Gaylor, assignors toPATENT oFF- lcs change of Standard Oil Development Company, acorporation of Delaware Application July 15, l193e, serial No. 90,668

2 Claims.

This invention relates to the production of butadiene. Morespecifically, it deals with a process involving dehydrogenation orcracking of normal butane to butylene, immediate removal of fixed gases,especially hydrogen, and dehydrogenation of the butylene under reducedpressure at a high temperature level and high feed rate.

Butadiene is a very desirable raw material for the production of asynthetic rubber which is in many respects superior to natural rubber,as for example, with respect to wear, oxidation, etc. However, the usesof such synthetic rubber have been restricted due to the high cost incomparison with natural rubber. The reason for such cost is that thecommercial process so far developed for the preparation of butadieneinvolves ve reactions, i. e. (1) vformation of acetylene, (2) conversionof acetylene to acetaldehyde, (3) condensation of the aldehyde to aldol,(4) hydrogenation of the aldol to butylene glycol, and (5) dehydrationof the glycol to butadiene. Even if good yields are obtained in theindividual reactions, Aconsiderable losses are incurred and handling andflxed charges are high. An object of this invention therefore is toaiord a, simple, eilicient method for producing butadiene. Furtherobjects will be apparent from the following disclosure.

'I'he process linvolved in the present invention consists incatalytically dehydrogenating n-butane (which is av common constituentof natural gas) to butylene, maintaining. a conversion of about 2060%,removing hydrogen and fixed gas (methane, ethane, etc.) from theresulting mixture, and dehydrogenating again in presence of a catalystunder a vacuum under conditions to give a 10'30% butadiene in the exitgas. The resulting reaction mixture is again freed from hydrogen andfixed gas, the butadiene removed, and the remaining C4 hydrocarbons 'arerecycled to the first step.

The dehydrogenation of normal butane to butadiene involves the followingtwo reactions:

With an active catalyst, excessive temperatur and sufficiently lowthroughput, it is possible to produce substantial amounts of butadienein one step by dehydrogenation of butane. 'I'his has been found to beimpractical since the conditions are so'severe as to cause the formationof cracked greatly lowering the efciency.

It is also -possible to convert butanesubstan'- pumped through linetially completely into butylene and cracked products in one step andthen to convert completely butylene into butadiene and cracked productsin a second step. However,l as illustrated by this invention,` such aprocess is not very practical because when substantially completeone-pass conversion of butane is carried out in one pass i somebutadiene is formed which causes rapid coking up of the catalyst in thesecond stage.

It has now been found that in the case of the first step given above,butadiene .formation is very low until a conversion of about iO-60% ofthe butane is reached, when the butadiene production increases at arapid rate.

Therefore, this invention involves the formation of butylene from butanein the first stage without substantial production of butadiene, and

the catalyst life in the second step is thereby greatly improved. It haslikewise been found that deterioration of catalyst is further preventedand eiciency improved if the conversion of butylene in the Second stageis not over Sil-40%.

The accompanying gure shows in diagrammatic sectional elevation apreferred embodiment of this invention. Butane from storage I is ledthrough line 2 into lcompressor 3 whereby it is compressed to a pressuresufiicient tomaintain it in the liquid phase at room temperature. Thispressure may be in the neighborhood of 25-80 lbs. per square inch gage.The butane is then I into heat exchanger 5, line 6 and thence intodehydrogenator 1. This vessel is preferably filled with adehydrogenating catalyst, such'as chromium oxide on alumina, andmaintained at a. temperature of about 900- 1200 F. At this stage,Ztl-40% of the butane is converted into butylene, and some slightcracking occurs .resulting in the production of a small amount of C1, Czand C: hydrocarbons, butthe main' constituent of the fixed gas ishydrogen. Upon leaving the dehydrogenator through line 8 the reactionmixture is cooled by the feed 'in heat exchanger 5, and led through line9 and cooler l0 into separator Il. The latter serves to separate the xedgas from the Ci hydrocarbons and may be a fractionating column fromwhich the fixed gases are bled at l2, and. the butylene and unconvertedbutane are drawn oil.' at line I3 where, the pressure is released atvalve I4, allowing the gaseous C hydrocarbons ,to pass throughdehydrogenator l5 which may be at atmospheric pressure although a vacuumof about 20 to 100 or even 200 mm. of mercury is preferably maintainedby vacuum pump I8 or similar means. Dehydrogenator Il is vmaintained ati run through'llines 45 and 38, into the original"l 1ooo-13oo F. and isnned with a dehydrogenation of the butylene to the extent of 2li-.40%.

Some butane is also dehydrogenated in this operation.

'The hot gases leaving vacuum' pump I6 are preferably quenched in aquenching tower I1 wherein Water or oil or any suitable quenching mediumis sprayed by means of pipe I8 and spray I9 over plates orl baiiies 20,leaving the tower through line 2|. After this operation-the cooledgases, now at atmospheric pressure, are submitted to any known step forthe removal of butadiene, such as a scrubber or extractor 22 throughwhich the water and/or other. extracting medium is run in fromline 23.The extract containing the dioleiin is withdrawn at 24 and passed into astripping still 25 or other separator whereby butadiene is bled off atthe top at 26 and Ithe solvent is removed as bottoms at 21 and pumped bypump 28 back to tower 22 through lines 29 and 23.

The dioleiin-free gases leaving extractor 22 are subsequently drawn oliat 30 and compressed by compressor v3I to liquefy. the C4 cut which isthen separated'from the fixed gas and hydrogen by fractionator orseparator 32, the xed gases being discharged at 33, the C4 cut and anyhigher hydrocarbons formed leaving the tower at 34. `At this point, themixture may be either returned to the butane dehydrogenator, the bu'-tylene dehydrogenator, or polymerizer, depending upon the extent of thedehydrogenation effected in vessels 1 and I5. If a high conversion tobutylene is effected in 1, and a lower conver-y sion to butadiene isobtained in I5, it is preferable to recycle the C4 mixture from 34through lines-35, 36 and 31 to dehydrogenator I5. 0n

the other hand, if a low conversion is obtained in 45 1 and asubstantially high conversion is effected in I5 Without substantialamounts of butylene remaining after removal of butadiene, it isdesirable to lead the C4 mixture through lines 36 and 38 into line 4with the original feed stock.

However, in the usual case, substantial amounts of butylene are presentin the reaction mixture after removal of the butadiene. In such case itis found best to lead the C4 mixture from line 35 through Yline 39 -intopolymerizing chamber 40 maintained at 250-325 F. and filled with 5565%sulfuric acid or similar polymerization catalyst, converting thebutylene into a polymer such as dimer and some trimer and higherpolymers which are removed through line 4I and fractionated ,inseparator 42 in which they are removed'from the butane which is takenoff at the top of the tower at 43',.c'ooled in cooler 44 and butane feedstock while the polymers leaving separator 42 at 46 are depolymerized tobutylene by heating in vessel 41 at'400-500 F. in presence of 4a clay ofthe Marsil type or similar depolymeriza- *tion catalyst,cooled by cooler48 and run through.

lines 49 andv 31 into the butylene dehydrogenator In order to providefor the removal-of undesirable higher boiling materials accumulated inthe reaction system, the reaction stream leaving separator 32 throughline 34 is intermittently led through line 50 into separator orfractionator 5I wherein the C4 hydroarbons are removed at 52, cooled atv53, and returned to line 35 through pipe 54, while the higher boilingundesirable ends are removed from the tower through line 55.

In some cases it is found desirable to introduce some hydrogen with thefeed stock entering dehydrogenator 1.4 This is conveniently accomplishedby compressing some of the hydrogen leaving separator II (through linesI2 and 56) by means of compressor 51 into line 58 and thence into feedline 6l for the butane -dehydrogenator,

while the excess hydrogen and fixed gas may be bled out or burnedfrom.line 59. With a very sensitive catalyst it is often desirable to dilutethe inlet feed gas at 6 with as much as 50% (more or less) of hydrogenat the beginning of the operation ln order to reduce coking, and togradually decrease this hydrogen concentration to 30, 20, 10 and even 5%or less after prolonged continuous operation. i

' Similarly, some ofthe hydrogen-containing reaction mixture leavingline 9 may be by-passed through line 60 to accomplish the same result indehydrogenator I5.

Provisions are made for withdrawing liquid polymers at 6I, 62 and63`a1thoug'h it is ordinarily Example 1 Normal butane at atmosphericpressure is' passed over a chromiumoxide-on-activated alumina catalystat 1112o F. and a contact time of 2.1 seconds. Under these conditions42% of the entering butane is converted to butylene per pass.v

A`fter removal of the hydrogen and iixed gas by compression of thegaseous mixture to lbs. per square inch gage, the liquid hydrocarbonremaining contains about 50% butylene. 'Ihis mixture is then passedvover chromium oxide on activated alumina at 10'70 F. and under 50 mm. ofHg pressure. 'I'he feed rate is 132 volumes of gas per volume ofcatalyst,per hour (0 C. .and '160 mm) (corresponding to a contact timeof 0.35 second under these conditions,` 35.4% ofthe butylene in the gasreacts producing a gas mixture which, upon subsequent removal of fixedgas contains about 18% of butadiene. o

The butadiene is removed by extraction of the liquid hydrocarbons withliquid ammonia or ethylene glycol, and the remaining mixture of butaneand butylenev are' passed into 60% sulfurie acid at 235-400 F. topolymerize the butylene., Upon distillation, the polymers removed asbottoms are cracked at 450 F. and depolymerized to butylene and returnedto the second dehydrogenation zone, while the overhead from the'stillconsisting substantially of butane is sent back for recycling throughthe iirst dehydrogenation zone. f y

. water and extracted with water followed by acid solution to removebutadiene,

cuprous chloride to about 50 lbs., the fixed gases then compressed areremoved and the remaining hydrocarbons boiling mainly in the Cirange arerecycled to the rst dehydrogenating tower. l

The foregoing description is not limited to any specific examples or toany theory of reaction but merely to the claims in which it is myintention to cover the invention as broadly as 4 art permits.

formed, separating fixed gases, polymerizing the butylene in theresidual hydrocarbons, separating the prior products in la sec-- Y ondstep under vacuum, removing the butadiene the polymers from recyclingthe butylene to the second dehydrogenation step heretofore described,and recycling the unpolymerized hydrocarbons to the rst dehydrogenationstep heretofore described.

' 2. Process for producing butadiene comprisingl dehydrogenating normalbutane in the presence of hydrogen in a, dehydrogenating stepiat' atleast atmospheric pressure, dehydrogenating the resulting products ina'second step under vacuum, removing the butadiene formed, separatingxed gases, polymerizing the butylene inthe residual hydrocarbons,separating tlie .polymers from the unpolymerized hydrocarbons,depolymerizing the polymers to butylene, recycling the butylene-to thesecond dehydrogenation step heretofore described, and recyclingtheunpolymerized hydrocarbons to the first dehydrogenationstepheretofore described.

PETER J. WIEZE'VICH. RAPHAEL ROSEN.

the unpolymerized hydrocar` bons, depolymerizing the polymers tobutylene,l

